Acrylic polymer particles, production process therefor, ink composition, and coating composition

ABSTRACT

Particles of an acrylic polymer comprising a constituent unit (A) derived from methyl methacrylate and a constituent unit (B) derived from a (meth)acrylic acid alkyl ester in which the alkyl group has 2 to 8 carbon atoms, wherein the particles having electrostatic buildup inhibition rate of 90 to 99.9° as obtained by a specific method.

This application is a divisional of U.S. Non-Provisional applicationSer. No. 15/941,946, filed on Mar. 30, 2018, which is a continuation ofPCT/JP2016/055431 that was filed on Feb. 24, 2016. This application isbased on and claims the benefit of priority of Japanese PatentApplication No. 2016-000090, filed on Jan. 4, 2016, and the entirecontents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to particles of an acrylic polymer thatare suitable for a coating material, ink, or the like, a process forproducing the particles of an acrylic polymer, an ink composition, and acoating composition.

BACKGROUND ART

As a method useful for producing particles of an acrylic polymer, asuspension polymerization method is known. According to the suspensionpolymerization method, slurry of an acrylic polymer after polymerizationis appropriately dehydrated and washed, and after subjecting it to astep like drying, particles of an acrylic polymer are produced. Theparticles of an acrylic polymer are used as a raw material of a coatingcomposition, a raw material of an ink composition, a binder for a copymachine toner, a binder for ceramic calcination, an intermediate rawmaterial of a thermoplastic resin, or the like.

With tendency of having low electric conductivity and large specificsurface area, the particles of an acrylic polymer have a property ofeasy electrostatic buildup. Because it is easy for the particles of anacrylic polymer with electrostatic buildup to have low fluidity, thereare cases in which blocking inside a pipe of a manufacturing plant orpoor sieve device passability is caused by them. Furthermore, there arealso cases of having a problem in handlability when the particles of anacrylic polymer are in a state of electrostatic buildup. Electrostaticbuildup may easily occur after a drying step of the particles of anacrylic polymer. Due to those reasons, a method for suppressingelectrostatic buildup during a step after the suspension polymerizationis suggested.

For example, a method of providing conductivity according to a chemicaltreatment of a surface of particles of an acrylic polymer, a method ofreducing friction among acrylic polymers by carrying out drying using avacuum dryer or the like so that the electrostatic buildup may hardlyoccur, a method of drying the particles of an acrylic polymer withhumidified air, a method of removing electrostatic buildup by carryingout an electric treatment of the particles of an acrylic polymer withelectrostatic buildup, or the like are suggested.

However, those methods are problematic in that large amounts of moneyare required for facility investment or operation, process management iscumbersome, production rate is slow, or the like.

Accordingly, as a method for convenient and low-cost production of theparticles of an acrylic polymer with excellent fluidity due tosuppressed electrostatic buildup, in Patent Literature 1, for example, amethod of washing the particles of an acrylic polymer after suspensionpolymerization with water in which electrolytes are dissolved at 1 to1000 ppm is described.

CITATION LIST Patent Literature

-   Patent Literature 1: JP 2003-306512 A

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

Meanwhile, the particles of an acrylic polymer are required to have notonly the fluidity but also the solubility in an organic solvent.However, the particles of an acrylic polymer that are obtained by themethod described in Patent Literature 1 have a problem that whitecloudiness is yielded when they are dissolved in an organic solvent liketoluene.

An object of the present invention is to provide particles of an acrylicpolymer having excellent fluidity due to suppressed electrostaticbuildup. Another object of the present invention is to provide particlesof an acrylic polymer which have excellent solubility in an organicsolvent. Still another object is to provide a process for producing theparticles of an acrylic polymer, an ink composition, and a coatingcomposition.

Means for Solving Problem

Namely, the present invention has the following embodiments.

-   [1] Particles of an acrylic polymer which contains a constituent    unit (A) derived from methyl methacrylate and a constituent unit (B)    derived from a (meth)acrylic acid alkyl ester in which the alkyl    group has 2 to 8 carbon atoms, the particles having electrostatic    buildup inhibition rate of 90 to 99.9% as obtained by the following    method:

(Method for obtaining electrostatic buildup inhibition rate)

According to HS K 7365:1999 “Plastics—Method for determination ofapparent density of material that can be poured from a specifiedfunnel”, volume density (A) of the particles of an acrylic polymer ismeasured. In addition, an anti-static agent is added in an amount of 0.1g per 100 mL of the particles of an acrylic polymer volume density (B)of a mixture obtained by sufficiently mixing them is measured, and theelectrostatic buildup inhibition rate is calculated based on thefollowing mathematical equation (1).Electrostatic buildup inhibition rate (%)=Volume density(A)/Volumedensity(B)×100  (1)

-   [2] The particles of an acrylic polymer described in above [1] which    a sodium element amount in the particles of an acrylic polymer is    3.5 to 50 ppm.-   [3] The particles of an acrylic polymer described in above [2] in    which the sodium element amount in the particles of an acrylic    polymer is 3.5 to 30 ppm.-   [4] The particles of an acrylic polymer described in above [1] in    which the particles have a mass average particle diameter of 100 to    1000 μm.-   [5] The particles of an acrylic polymer described in above [1] in    which the particles of an acrylic polymer further contain a    constituent unit (C) derived from α,β-unsaturated carboxylic acid.-   [6] Particles of an acrylic polymer which contains a constituent    unit (A) derived from methyl methacrylate and a constituent unit (B)    derived from (meth)acrylic acid alkyl ester in which the alkyl group    has 2 to 8 carbon atoms, the particles having a sodium element    amount of 3.5 to 50 ppm.-   [7] The particles of an acrylic polymer described in above [6] in    which the sodium element amount in the particles of an acrylic    polymer is 3.5 to 30 ppm.-   [8] The particles of an acrylic polymer described in above [6] in    which the particles have a mass average particle diameter of 100 to    1000 μm.-   [9] The particles of an acrylic polymer described in above [6] in    which the particles of an acrylic polymer further contain a    constituent unit (C) derived from α,β-unsaturated carboxylic acid.-   [10] A process for producing particles of an acrylic polymer    described in any one of [1] to [9] including a step of washing the    acrylic polymer obtained by suspension polymerization so as to have    a sodium element amount of 3.5 to 50 ppm.-   [11] The process for producing particles of an acrylic polymer    described in [10] in which a dispersion agent containing sodium    element is used for the suspension polymerization.-   [12] The process for producing particles of an acrylic polymer    described in [11] in which a use amount of the dispersion agent is    an amount allowing that the sodium element amount contained in the    dispersion agent is 0.0009 to 0.004 part by mass relative to 100    parts by mass of a raw material monomer of the particles of an    acrylic polymer.-   [13] The process for producing particles of an acrylic polymer    described in [10] in which a dispersion aid containing sodium    element is used for the suspension polymerization.-   [14] The process for producing particles of an acrylic polymer    described in [13] in which a use amount of the dispersion aid is an    amount allowing that the sodium element amount contained in the    dispersion aid is 0.06 to 0.35 part by mass relative to 100 parts by    mass of a raw material monomer of the particles of an acrylic    polymer.-   [15] The process for producing particles of an acrylic polymer    described in [10] in which the washing is carried out by using an    aqueous solution of a sodium element-containing compound.-   [16] The process for producing particles of an acrylic polymer    described in [15] in which a use amount of the aqueous solution of a    sodium element-containing compound is an amount allowing that the    sodium element amount contained in the aqueous solution of a sodium    element-containing compound is 0.03 to 0.1 part by mass relative to    100 parts by mass of the acrylic polymer.-   [17] The process for producing particles of an acrylic polymer    described in [15] in which mass of the aqueous solution of a sodium    element-containing compound to be used for the washing is 1 to 3    times the acrylic polymer.-   [18] An ink composition containing the particles of an acrylic    polymer described in any one of [1] to [9].-   [19] A coating composition containing the particles of acrylic    polymer described in any one of [1] to [9],-   [20] The coating composition described in [19] in which use of the    coating composition is use for container, marine use, or use for    road marking.

Effect of the Invention

According to the present invention, particles of an acrylic polymerhaving excellent fluidity due to suppressed electrostatic buildup, aprocess for producing the particles of an acrylic polymer, an inkcomposition, and a coating composition can be provided.

MODE(S) FOR CARRYING OUT THE INVENTION

“Particles of an Acrylic Polymer”

The acrylic polymer constituting the particles of an acrylic polymer ofthe present invention (hereinbelow, simply described as an “acrylicpolymer”) contains the constituent unit (A) derived from methylmethacrylate and the constituent unit (B) derived from a (meth)acrylicacid alkyl ester in which the alkyl group has 2 to 8 carbon atoms.

Furthermore, in the present invention, the term “(meth)acrylic acid” isa general name of acrylic acid and methacrylic acid.

Examples of the (meth)acrylic acid alkyl ester in which the alkyl grouphas 2 to 8 carbon atoms include ethyl acrylate, n-butyl acrylate,i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, ethylmethacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butylmethacrylate, and 2-ethylhexyl methacrylate. Among them, from theviewpoint of having excellent weather resistance in hardened material ofan ink composition or a coating composition containing particles of anacrylic polymer to be obtained and also easy obtainability, n-butylmethacrylate is preferable.

They may be used in combination of two or more kinds thereof.

It is possible that the acrylic polymer further contains the constituentunit (C) derived from α,β-unsaturated carboxylic acid.

The α,β-unsaturated carboxylic acid is not particularly limited as longas it can be copolymerized with methyl methacrylate and (meth)acrylicacid alkyl ester in which the alkyl group has 2 to 8 carbon atoms, andexamples thereof include acrylic acid, methacrylic acid, maleic acid,fumaric acid, and itaconic acid.

They may be used in combination of two or more kinds thereof.

It is possible that the acrylic polymer further contains a constituentunit (D) other than the constituent unit (A), the constituent unit (B),and the constituent unit (C).

A monomer as a source of the constituent unit (D) is not particularlylimited as long as it can be copolymerized with methyl methacrylate and(meth)acrylic acid alkyl ester in which the alkyl group has 2 to 8carbon atoms. Examples of the monomer include acrylic acid esters suchas methyl acrylate, lauryl acrylate; dodecyl acrylate, stearyl acrylate;phenyl acrylate; benzyl acrylate, glycidyl acrylate; 2-hydroxylethylacrylate; 2-hydroxylpropyl acrylate, 2-methoxy ethyl acrylate;2-ethoxyethyl acrylate, or phenoxyethyl acrylate; methacrylic acidesters such as lauryl methacrylate, dodecyl methacrylate; stearylmethacrylate, cyclohexyl methacrylate; isobornyl methacrylate; phenylmethacrylate, benzyl methacrylate, glycidyl methacrylate,2-hydroxylethyl methacrylate, 2-hydroxylpropyl methacrylate,2-methoxyethyl methacrylate, 2-ethoxyethyl methacrylate, or phenoxyethylmethacrylate; maleimides such as N-phenylmaleimide orN-cyclohexylmaleimide; aromatic vinyl compounds such as styrene,o-methylstyrene, m-methylstyrene, p-methylstyrene, or α-methylstyrene;polymerizable amides such as acrylamide or methacrylamide, anddialkylaminoethyl (meth)acrylates such as dimethylaminoethyl acrylate,diethylaminoethyl acrylate, dimethylaminoethyl methacrylate, ordiethylaminoethyl methacrylate.

They may be used in combination of two or more kinds thereof.

Mass ratio between the constituent unit (A) and the constituent unit (B)in the acrylic polymer is, in terms of the constituent unit (A): theconstituent unit (B), preferably 10:90 to 90:10, more preferably 20:80to 80:20, and even more preferably 30:70 to 70:30. As the mass ratio iswithin this range, favorable performance balance between coating filmhardness and wetting property on a surface of a coating subject isobtained when an ink composition or a coating composition is preparedwith the polymer. In the acrylic polymer, the total content of theconstituent unit (A) and the constituent unit (B) is preferably 80 to100% by mass, more preferably 90 to 100% by mass, and even morepreferably 95 to 100% by mass in 100% by mass of the total of allconstituent units.

In a case in which the acrylic polymer contains the constituent unit(C), content of the constituent unit (C) is preferably 0.1 to 2% by massin 100% by mass of the total of all constituent units. Content of theconstituent unit (C) is more preferably 1.5% by mass or less, and evenmore preferably 1.2% by mass or less. As the content of the constituentunit (C) is the same or less than the aforementioned upper limit, adecrease in the fluidity of the particles of an acrylic polymer, whichis caused by electrostatic buildup, is suppressed more so that anexcellent pigment dispersion property is obtained when an inkcomposition or a coating composition is prepared with the polymer.

In a case in which the acrylic polymer contains the constituent unit(D), content of the constituent unit (D) is preferably 10% by mass orless, more preferably 5% by mass or less, and even more preferably 1% bymass or less in 100% by mass of the total of all constituent units. Asthe content of the constituent unit (D) is the same or less than theaforementioned upper limit, an excellent copolymerization property andexcellent solvent solubility are obtained. In the present specification,ratio of each constituent unit of the acrylic polymer indicates a valuewhich is calculated from the mass of an each monomer used as a rawmaterial.

The particles of an acrylic polymer of the present invention haveelectrostatic buildup inhibition rate of 90 to 99.9%, in which theelectrostatic buildup inhibition rate is obtained by the methoddescribed below. As the electrostatic buildup inhibition rate is withinthe above range, excellent fluidity is obtained. From the viewpoint offurther enhancing the fluidity, the electrostatic buildup inhibitionrate is preferably 95% or higher.

(Method for Obtaining Electrostatic Buildup Inhibition Rate)

According to JIS K 7365:1999 “Plastics—Method for determination ofapparent density of material that can be poured from a specifiedfunnel”, volume density (A) of the particles of an acrylic polymer ismeasured. In addition, an anti-static agent is added in an amount of 0.1g per 100 mL of the particles of an acrylic polymer, and volume density(B) of a mixture obtained by sufficiently mixing them is measured. As ananti-static agent, “SILPHONITE M-1” or “SILTON A”, which is activesilica manufactured by Mizusawa Industrial Chemicals Ltd., are suitable,for example. The electrostatic buildup inhibition rate is calculatedfrom the measured volume density (A) and volume density (B) based on thefollowing mathematical equation (1).Electrostatic buildup inhibition rate (%)=Volume density(A)/Volumedensity(B)×100  (1)

The sodium element amount in the particles of an acrylic polymer of thepresent invention is preferably 3.5 to 50 ppm, more preferably 3.5 to 40ppm, even more preferably 3.5 to 30 ppm, and particularly preferably 5ppm to 30 ppm. As the sodium element amount is the same or more than theabove lower limit, electrostatic buildup is suppressed more so that thefluidity is further enhanced. The effect of having enhanced fluiditytends to increase in accordance with an increase in the sodium elementamount. However, as the sodium element amount is more than 50 ppm, theeffect of suppressing electrostatic buildup tends to get saturated, thusyielding a limiting point of the fluidity enhancement. Furthermore, asthe sodium element amount increases unnecessarily, purity of theparticles of an acrylic polymer is impaired.

The sodium element in the particles of an acrylic polymer originatesfrom sodium salts or the like that are included in a dispersion agent, adispersion aid, or a washing liquid used for producing the particles ofan acrylic polymer.

The sodium element in the particles of an acrylic polymer is measured byusing a high frequency inductively coupled plasma (ICP) light emissionspectrophotometer.

The average particle diameter of the particles of an acrylic polymer ispreferably 100 to 1000 μm, and more preferably 120 to 700 μm. As theaverage particle diameter is the same or more than the above lowerlimit, a decrease in the fluidity caused by electrostatic buildup issuppressed more.

The average particle diameter indicates a value which is calculated froma particle size distribution obtained by measuring a mass-based particlesize distribution using laser diffraction/scattering type particle sizedistribution analyzer after dispersing the particles of an acrylicpolymer in water (mass average particle diameter).

Moisture content in the particles of an acrylic polymer is preferably 5%or less and more preferably 2% or less. Furthermore, the moisturecontent is calculated from mass of the particles of an acrylic polymerwhen the moisture content of the particles of an acrylic polymer afterdehydration step followed by drying for 2 hours at 105° C. is set at 0%.

<Method for Production>

The particles of an acrylic polymer can be produced as described below,for example.

The process for producing the particles of an acrylic polymer of thisembodiment has a polymerization step, a first dehydration step, awashing step, a second dehydration step, and a drying step.

(Polymerization Step)

The polymerization step is a step for obtaining an acrylic polymer bysuspension polymerization of methyl methacrylate, (meth)acrylic acidalkyl ester in which the alkyl group has 2 to 8 carbon atoms, and, ifnecessary, α,β-unsaturated carboxylic acid or an optional monomer.

As for the method for suspension polymerization, a well-known method canbe employed, and, for example, there is a method in which methylmethacrylate, (meth)acrylic acid alkyl ester in which the alkyl grouphas 2 to 8 carbon atoms, and, if necessary, α,β-unsaturated carboxylicacid or an optional monomer are polymerized, in the presence of apolymerization aid, in water in a vessel having polymerizationtemperature control and stirring functions.

Examples of the polymerization aid include a polymerization initiator, achain transfer agent, a dispersion agent, and dispersion aid.

Examples of the polymerization initiator include2,2′-azobisisobutyronitrile, 2,2′-azobis (2-methylbutyronitrile),benzoyl peroxide, and lauroyl peroxide.

Examples of the chain transfer agent include n-dodecyl mercaptan,octylthioglycolate, and α-methylstyrene dimer.

As for the dispersion agent, a surface active agent capable of stablydispersing a monomer in water can be mentioned, and specific examplesthereof include a copolymer of sodium 2-sulfoethyl methacrylate,potassium methacrylate, and methyl methacrylate, a copolymer of sodium3-sulfopropyl methacrylate and methyl methacrylate, a copolymer ofsodium methacrylate and methacrylic acid, polyvinyl alcohol, polyvinylpyrrolidone, hydroxylethylcellulose and hydroxylpropylcellulose.

Examples of the dispersion aid include sodium sulfate, sodium carbonate,sodium dihydrogen phosphate, disodium hydrogen phosphate, potassiumchloride, calcium acetate, magnesium sulfate, and manganese sulfate.

To obtain the particles of an acrylic polymer in which a sodium elementamount is 3.5 to 50 ppm, it is preferable to use, as a dispersion agent,those containing sodium like a copolymer of sodium 2-sulfoethylmethacrylate, potassium methacrylate, and methyl methacrylate, acopolymer of sodium 3-sulfopropyl methacrylate and methyl methacrylate,a copolymer of sodium methacrylate and methacrylic acid, and the likethat are described above. Furthermore, it is preferable to use, as adispersion aid, those containing sodium like sodium sulfate, sodiumcarbonate, sodium dihydrogen phosphate, disodium hydrogen phosphate, andthe like.

The use amount of the dispersion agent containing sodium is an amountallowing that the sodium element amount contained in the dispersionagent is preferably 0.0009 to 0.004 part by mass, and more preferably0.0012 to 0.003 part by mass relative to 100 parts by mass of the totalraw material monomers of an acrylic polymer.

The use amount of the dispersion aid containing sodium is an amountallowing that the sodium element amount contained in the dispersion aidis preferably 0.06 to 0.35 part by mass, and more preferably 0.14 to0.28 part by mass relative to 100 parts by mass of the total rawmaterial monomers of an acrylic polymer.

As the use amount of the dispersion agent or dispersion aid containingsodium is within the aforementioned range, it becomes easier to obtainthe particles of an acrylic polymer in which a sodium element amount is3.5 to 50 ppm.

The acrylic polymer obtained by suspension polymerization is obtained ina slurry state.

In general, the particles of an acrylic polymer have a bead shape thatis close to true sphere. Although the particle size of the particles ofan acrylic polymer has a distribution, it is preferable that the massaverage particle diameter is set within a range of 10 to 1000 μm.

(First Dehydration Step)

The first dehydration step is a step in which the slurry aftersuspension polymerization is dehydrated and the particles of an acrylicpolymer are separated from a reaction solution.

For the dehydration, various kinds of a dehydrator can be used. Forexample, a centrifuge dehydrator, a centrifuge separator, a device forremoving water by suction on porous belt, or the like can be suitablyselected and used.

(Washing Step)

The washing step is a step of washing in which the particles of anacrylic polymer obtained by suspension polymerization are washed suchthat electrostatic buildup inhibition rate of the particles of anacrylic polymer to be obtained by final drying is 90 to 99.9%. Theparticles of an acrylic polymer which have electrostatic buildupinhibition rate of 90 to 99.9% can be obtained by carrying out, forexample, washing such that the sodium element amount of the particles ofan acrylic polymer, which are obtained by final drying, is 3.5 to 50ppm.

According to the washing step, not only the purity of the particles ofan acrylic polymer is increased but also particles of an acrylic polymerwhich have the sodium element amount of 3.5 to 50 ppm are obtained.

As for the washing method, there is a method of adding a washingsolution to particles of an acrylic polymer that are dehydrated in thefirst dehydration step followed by re-slurrying of the acrylic polymerwith stirring and mixing, a method of carrying out washing by, afterperforming the first dehydration step in a dehydrator which also has awashing function, adding continuously a washing solution or the like. Itis also possible that the washing is carried out by combining thosewashing methods.

Type or amount of the washing solution can be selected so as to achievethe purpose of the washing step. Examples of a washing agent includewater (ion exchange water, distilled water, purified water, or thelike), aqueous solution in which sodium salts are dissolved (aqueoussolution of Na salts, or the like), or the like.

In a case in which a dispersion agent or a dispersion aid containingsodium is used during the polymerization step, for example, it ispreferable to use water or an aqueous solution of Na salts as a washingsolution. In particular, when the sodium element amount is high in theparticles of an acrylic polymer before washing, it is preferable to usewater as a washing solution, and when the sodium element amount is lowin the particles of an acrylic polymer before washing, it is preferableto use an aqueous solution of Na salts as a washing solution.

In a case in which a dispersion agent or a dispersion aid containing nosodium is used during the polymerization step, it is preferable to usean aqueous solution of Na salts as a washing solution.

Furthermore, in a case in which the sodium element amount is more than50 ppm in the particles of an acrylic polymer after washing by using anaqueous solution of Na salts, washing is carried out again by usingwater or the like so that the sodium element amount can be within arange of 3.5 to 50 ppm.

Examples of the sodium salts that are used for an aqueous solution of Nasalts include sodium chloride, sodium sulfate, sodium acetate, sodiumisethionate, sodium, p-toulene sulfonate, and sodium carbonate.

Sodium concentration of the aqueous solution of Na salts is preferablyis 500 to 2000 ppm, and more preferably 600 to 1000 ppm. As the sodiumconcentration is 500 ppm or more, the acrylic polymer can be providedwith a sufficient anti-static property. As a result, the electrostaticbuildup can be easily suppressed so that the fluidity is enhanced more.The effect of having enhanced fluidity tends to increase in accordancewith an increase in the sodium salt concentration. However, as thesodium salt concentration is 2000 ppm or more, the effect of suppressingelectrostatic buildup tends to get saturated, thus yielding a limitingpoint of the fluidity enhancement. Furthermore, as the sodium salts thatare adhered and remained on a surface of the particles of an acrylicpolymer increases, an impairment of the purity of the particles of anacrylic polymer is caused.

The amount of the washing solution for the washing step is preferablysuch that the particles of an acrylic polymer and the washing solutionare present at 1:1 or higher in terms of the mass ratio (acrylicpolymer:washing solution). Accordingly, the sodium salt amount in thewashing solution can be easily reflected on a sodium element content ofthe acrylic polymer after washing, and thus the sodium element contentin the particles of an acrylic polymer can be easily controlled.

As a method for producing industrially an aqueous solution of Na saltswith predetermined concentration which is used for the washing, there isa method in which water and sodium salts are mixed with each other atpredetermined ratio in a tank having stirrer to produce in advance ahigh-concentration aqueous solution of Na salts, and a certain amount ofthe aqueous solution of Na salts is transported to a supply line withflowing water to mix the high-concentration aqueous solution of Na saltswith water. It is favorable that the washing is carried out by supplyingthe resulting mixture via a supply line to the particles of an acrylicpolymer.

Number of the washing is not particularly limited, and it can be carriedout once or twice or more as long as the sodium element amount in theparticles of an acrylic polymer becomes 3.5 to 50 ppm.

(Second Dehydration Step)

The second dehydration step is a step in which the particles of anacrylic polymer after the washing step are dehydrated.

For the dehydration, various dehydrators can be used, and thoseexemplified for explaining the first dehydration step can be mentioned,for example.

As for the dehydrator used for the first dehydration step and thedehydrator used for the second dehydration step, one dehydrator may beused for both steps, two dehydrators of the same type may be used foreach dehydration step, or dehydrators of different type may be used foreach dehydration step. Selection can be made suitably to meet thepurpose in view of product quality, cost related to facility investment,productivity, cost required for operation, or the like. When balancebetween product quality and production rate is taken importantly, it ispreferable to use a dehydrator exclusive for each dehydration step.

(Drying Step)

The drying step is a step for drying the particles of an acrylic polymerafter the second dehydration step.

Water remains on a surface of the particles of an acrylic polymer afterthe second dehydration step. Furthermore, inside of the acrylic polymeris in a state of almost saturated water absorption. Due to such reasons,it is preferable to dry the polymer to further decrease the moisturecontent in the acrylic polymer.

For the drying, various kinds of a dryer can be used, and examplesinclude carrying out the drying by heating under reduced pressure,carrying out the drying simultaneously supplying the particles of anacrylic polymer into a pipe by using heated air, and carrying out thedrying while fluidizing the particles of an acrylic polymer at the topside by injecting heated air from the bottom side of a porous plate.

The drying step is carried out such that the moisture content in theacrylic polymer after the drying step is preferably 5% or less, and morepreferably 2% or less.

<Working Effects>

The particles of an acrylic polymer of the present invention explainedabove have electrostatic buildup inhibition rate of 90 to 99.9%, andthus have excellent fluidity. In particular, as the sodium elementamount is 3.5 to 50 ppm, the electrostatic buildup is furthersuppressed, and thus the fluidity can be enhanced more. As such, it isexpected to resolve the problem of clogging in a pipe through which theparticles of an acrylic polymer are transported. Furthermore, theparticles of a powder-like acrylic polymer after a drying treatment maybe sometimes get passed through a sieve device under the purpose ofcollecting only the particles with desired particle size, and animprovement in passability is expected therefor. Furthermore, in termsof the handling of the particles of an acrylic polymer at destination,it is unlikely to have a problem of poor fluidity. Still furthermore,since the particles of an acrylic polymer of the present invention havesuppressed electrostatic buildup, flame ignition hardly occurs thereon.

Furthermore, according to the process for producing the particles of anacrylic polymer of the present invention, particles of a powder-likeacrylic polymer with excellent fluidity can be produced conveniently atlow cost due to suppressed electrostatic buildup.

Furthermore, the process for producing the particles of an acrylicpolymer of the present invention is not limited to the embodiment whichis described above. For example, although a second dehydration step iscarried out in the embodiment that is described above, such secondarydehydration step may be omitted. Furthermore, it is also possible that,when the sodium element amount in the acrylic polymer obtained by thepolymerization step is 3.5 to 50 ppm, the washing step may be omitted.However, in view of the purpose of increasing the purity of the acrylicpolymer by removing unreacted monomers or the like, the washing step ispreferably carried out even when the sodium element amount in theacrylic polymer obtained by the polymerization step is 3.5 to 50 ppm.

Furthermore, each step described above may be continuously carried out,or the polymerization step and washing step may be carried out indifferent areas.

<Use>

The particles of an acrylic polymer of the present invention can be usedas a raw material of an ink composition, a raw material of a coatingcomposition, a binder for a copy machine toner, a binder for ceramiccalcination, an intermediate raw material of a thermoplastic resin, orthe like. They are particularly suitable as a raw material of an inkcomposition or a raw material of a coating composition.

“Ink Composition”

The ink composition of the present invention contains the particles ofan acrylic polymer of the present invention.

The ink composition of the present invention is obtained by mixing, forexample, the particles of an acrylic polymer of the present inventionwith a pigment, an organic solvent, and, if necessary, an optionalcomponent.

As for the pigment, a well-known pigment used as a raw material of anink can be mentioned.

As for the organic solvent, a well-known organic solvent used as a rawmaterial of an ink can be mentioned.

As for the optional component, various kinds of well-known additivesthat are used as a raw material of an ink can be mentioned.

“Coating Composition”

The coating composition of the present invention contains the particlesof an acrylic polymer of the present invention.

The coating composition of the present invention can be used as acoating material for container, a coating material for marine use, or acoating material for road marking, for example.

The coating material for marine use indicates a coating material forcoating a deck of a ship or the like.

The coating material for road marking indicates a coating material fordisplaying a road sign or the like on a road.

When the coating composition of the present invention is used for acontainer, a coating composition obtained by mixing the particles of anacrylic polymer of the present invention with a pigment, calciumcarbonate, chlorinated paraffin, an organic solvent, and, if necessary,an optional component is suitable.

When the coating composition of the present invention is used for marineuse, it is obtained by mixing the particles of an acrylic polymer of thepresent invention with a pigment, an organic solvent, and, if necessary,an optional component.

When the coating composition of the present invention is used for roadmarking, it is obtained by mixing the particles of an acrylic polymer ofthe present invention with a pigment, calcium carbonate, an organicsolvent, and, if necessary, an optional component.

As for the pigment, a well-known pigment used as a raw material of acoating material can be mentioned.

As for the organic solvent, a well-known organic solvent used as a rawmaterial of a coating material can be mentioned.

As for the optional component, various kinds of well-known additivesthat are used as a raw material of a coating material can be used inaccordance with the use of the coating composition.

EXAMPLES

Hereinbelow, the present invention is more specifically explained inview of Examples. However, the present invention is not limited thereto.

Measurement and evaluation of each physical property in Examples andComparative Examples were carried out according to the followingmethods.

Furthermore, the dispersion agents that are used in Examples andComparative Examples were prepared according to the following method.

[Measurement⋅Evaluation]

<Measurement of Sodium Element Amount>

The particles of an acrylic polymer (0.15 g) were collected in aplatinum crucible and heated on a hot plate over 1 hour from 150° C. to540° C. and also for 30 minutes at 540° C. Subsequently, the particlesof an acrylic polymer were turned into ash in a muffle furnace at 575°C. for 1 hour. To the resultant, 250 μL of 1% by mass aqueous solutionof nitric acid were added for dissolution, and dilution to 25 mL wasmade with ultra pure water. The diluted product was applied to an ICPlight emission spectrophotometer to measure the sodium element amount(Na element amount). Furthermore, the measurement conditions are asdescribed in the followings.

(ICP Measurement Conditions)

-   -   Apparatus: iCAP 6500 manufactured by Thermo Fischer Scientific        Inc.    -   RF power: 750 w    -   Pump flow rate: 50 rpm    -   Assisting gas flow rate: 1 L/min    -   Nebulizer gas flow rate: 0.5 L/min    -   Coolant gas flow rate: 12 L/min    -   Purge gas flow rate: Normal    -   Wavelength for measurement: 589.592 (nm)

<Measurement of Average Particle Diameter>

The particles of an acrylic polymer were dispersed in water, and byusing “LA-910”, which is a laser diffraction/scattering type particlesize distribution analyzer manufactured by HORIBA, Ltd., mass-basedparticle size distribution was measured and mass average particlediameter was obtained from the obtained particle size distribution.

<Evaluation of Electrostatic Buildup Inhibition Rate>

According to JIS K 7365:1999 “Plastics—Method for determination ofapparent density of material that can be poured from a specifiedfunnel”, volume density (A) of the particles of an acrylic polymer wasmeasured. In addition, an anti-static agent (“SILPHONITE M-1”manufactured by Mizusawa Industrial Chemicals Ltd.) was added in anamount of 0.1 g per 100 mL of the particles of an acrylic polymer,volume density (B) of a mixture obtained by sufficiently mixing them wasmeasured, and the electrostatic buildup inhibition rate was calculatedbased on the equation (1) shown below. Furthermore, when the measurementis made without using an anti-static agent, there is generally atendency of having smaller volume density as caused by electrostaticrepulsion, and, when the measurement is made with use of an anti-staticagent, there is a tendency of having higher volume density as caused byreduced electrostatic repulsion. Namely, as the electrostaticitydecreases even without using an anti-static agent (that is, aselectrostatic buildup is suppressed more), a smaller change in thevolume density between a case before the addition of an anti-staticagent and a case after the addition of an anti-static agent is yielded,and the electrostatic buildup inhibition rate obtained by the followingmathematical formula (1) gets closer to 100%.Inhibition rate (%)=Volume density(A)/Volume density(B)×100  (1)

<Evaluation of Fluidity>

The fluidity of the particles of an acrylic polymer was measured asfollows; a powder funnel made of polyvinyl chloride, which has a mouthdiameter of 15 cm and a foot diameter of 1 cm, was used, and while thefunnel is fixed, 30 g of the particles of an acrylic polymer were addedto the funnel, and the evaluation was made in view of the falling stateof the particles.

(Evaluation Criteria)

-   -   A: The entire amount of the particles had fallen continuously.    -   B: Particle clogging had occurred during the process so that not        all of the entire amount had fallen.

<Evaluation of Solubility of Particles of Acrylic Polymer in Toluene>

Toluene (40 g) was added to a flask. While stirring it at roomtemperature using a stirrer, the particles of an acrylic polymer (60 g)were added thereto in small portions. After stirring them for 2 hours at60° C., the solubility was determined by naked eye observation based ontransparency of the solution.

(Evaluation Criteria)

-   -   A: The solution was transparent and excellent solubility was        obtained.    -   B: There was just slight white cloudiness of the solution, and        the solubility was good.    -   C: There was white cloudiness of the solution, and the        solubility was poor.

[Preparation of Dispersion Agent (1)]

In a polymerization device equipped with a stirrer, a condenser, and athermometer, 1230 part by mass of deionized water, 60 part by mass ofsodium 2-sulfoethyl methacrylate, 10 parts by mass of potassiummethacrylate, and 12 parts by mass of methyl methacrylate were addedfollowed by stirring. Under nitrogen purging inside the polymerizationdevice, the polymerization temperature was increased to 50° C., 0.08part by mass of 2,2′-azobis (2-methylpropionamidin) dihydrochloride wasadded as a polymerization initiator, and the polymerization temperaturewas further increased to 60° C. Simultaneously with the addition of apolymerization initiator, methyl methacrylate was added continuously for75 minutes at rate of 0.24 part by mass/min by using a dropping pump.After maintaining it for 6 hours at polymerization temperature of 60°C., cooling to room temperature was carried out to obtain dispersionagent (1). Solid content in the dispersion agent (1) was found to be7.5% by mass.

Example 1

To a polymerization device equipped with a stirrer, a condenser, and athermometer, a monomer mixture in which 39.8 part by mass of methylmethacrylate, 60 part by mass of n-butyl methacrylate, and 0.2 part bymass of methacrylic acid are homogeneously dissolved, and 200 part bymass of pure water in which 0.25 part by mass of 2,2′-azobis(2-methylbutyronitrile) as a polymerization initiator, 0.3 part by massof n-dodecylmercaptan as a chain transfer agent, 0.8 part by mass of thedispersion agent (1), and 1.0 part by mass of sodium sulfate as adispersion aid are homogeneously dissolved were added, and nitrogenpurging was carried out under stirring. After that, suspensionpolymerization was initiated at 75° C. After detecting an exothermicpeak of the polymerization, the polymerization was further carried outfor 30 minutes at 80° C. (polymerization step).

Subsequently, the inside of the furnace was cooled to room temperature.One third of the amount of the generated slurry was collected, and thendehydrated by using a centrifuge type dehydrator (dehydration step).

The obtained particles of an acrylic polymer and an aqueous solution ofsodium sulfate as a washing solution in which the sodium sulfateconcentration is 1000 ppm were added to a washing bath such that theyare present at 1:2 in terms of the mass ratio (particles of an acrylicpolymer:washing solution). After carrying out washing by stirring andmixing for 20 minutes (washing step), the resultant was dehydrated byusing a centrifuge dehydrator (dehydration step).

Subsequently, the dehydrated particles of an acrylic polymer were addedto a fluid bath type dehydrator of which internal temperature is set at50° C., and the particles were dried to have moisture content of 2% orless (drying step). Furthermore, the moisture content was calculatedfrom the mass of an acrylic polymer after the drying step, when theparticles of an acrylic polymer after the dehydration step are dried for2 hours at 105° C. and the moisture content of the resulting acrylicpolymer is set at 0%.

Na element amount and average particle diameter were then measured forthe particles of a powder-like acrylic polymer which have been obtainedas described above, and the evaluation was made for electrostaticbuildup inhibition rate, fluidity, and solubility in toluene. Theresults are shown in Table 1.

Example 2

Particles of a powder-like acrylic polymer were produced in the samemanner as Example 1 except that number of the washing step is modifiedto 3. Various kinds of measurements and evaluations were then carriedout. The results are shown in Table 1. Furthermore, for each washingstep, the washing solution was changed to a non-used solution.

Example 3

Particles of a powder-like acrylic polymer were produced in the samemanner as Example 1 except that ion exchange water is used as thewashing solution. Various kinds of measurements and evaluations werethen carried out. The results are shown in Table 1.

Example 4

Particles of a powder-like acrylic polymer were produced in the samemanner as Example 1 except that ion exchange water is used as thewashing solution and number of the washing step is modified to 3.Various kinds of measurements and evaluations were then carried out. Theresults are shown in Table 1. Furthermore, for each washing step, thewashing solution was changed to a non-used solution.

Example 5

Particles of a powder-like acrylic polymer were produced in the samemanner as Example 2 except that the use amount of sodium sulfate in thepolymerization step is modified to 0.2 part by mass. Various kinds ofmeasurements and evaluations were then carried out. The results areshown in Table 1.

Example 6

Particles of a powder-like acrylic polymer were produced in the samemanner as Example 5 except that the use amount of the dispersion agent(1) in the polymerization step is modified to 0.2 part by mass. Variouskinds of measurements and evaluations were then carried out. The resultsare shown in Table 1.

Example 7

Particles of a powder-like acrylic polymer were produced in the samemanner as Example 4 except that the use amount of methyl methacrylate inthe polymerization step is modified to 40 part by mass and methacrylicacid is not used. Various kinds of measurements and evaluations werethen carried out. The results are shown in Table 1.

Comparative Example 1

Particles of a powder-like acrylic polymer were produced in the samemanner as Example 4 except that, in the polymerization step, the useamount of the dispersion agent (1) is modified to 0.2 part by mass andthe use amount of sodium sulfate is modified to 0.2 part by mass.Various kinds of measurements and evaluations were then carried out. Theresults are shown in Table 1.

Comparative Example 2

Particles of a powder-like acrylic polymer were produced in the samemanner as Example 4 except that the use amount of sodium sulfate in thepolymerization step is modified to 0.2 part by mass. Various kinds ofmeasurements and evaluations were then carried out. The results areshown in Table 1.

Comparative Example 3

Particles of a powder-like acrylic polymer were produced in the samemanner as Comparative Example 1 except that the use amount of sodiumsulfate in the polymerization step is modified to 1.0 part by mass andwashing is not carried out. Various kinds of measurements andevaluations were then carried out. The results are shown in Table 1.

Comparative Example 4

Particles of a powder-like acrylic polymer were produced in the samemanner as Example 1 except that, in the polymerization step, the useamount of the dispersion agent (1) is modified to 0.1 part by mass andthe use amount of sodium sulfate is modified to 0.6 part by mass, and,in the washing step, concentration of an aqueous solution of sodiumsulfate is modified to 400 ppm. Various kinds of measurements andevaluations were then carried out. The results are shown in Table 1.

TABLE 1 Na element Electrostatic Dispersion amount of buildup AverageAcrylic agent (1) Dispersion Method for washing acrylic inhibitionparticle polymer Monomer [part aid [part Number polymer rate Solubilitydiameter composition by mass] by mass] Washing solution (times) [ppm][%] Fluidity in toluene [mm] Example 1 Methyl methacrylic 0.8 1.0 Na₂SO₄aqueous 1 41 97 A B 139 acid/n-butyl solution methacrylate/ [1000 ppm]Example 2 methacrylic 0.8 1.0 Na₂SO₄ aqueous 3 35 96 A B 138 acid =39.8/60/0.2 solution [1000 ppm] Example 3 0.8 1.0 Ion exchange 1 19 94 AA 130 water Example 4 0.8 1.0 Ion exchange 3 7.3 92 A A 135 waterExample 5 0.8 0.2 Na₂SO₄ aqueous 3 20 94 A A 220 solution [1000 ppm]Example 6 0.2 0.2 Na₂SO₄ aqueous 3 17 93 A A 269 solution [1000 ppm]Example 7 Methyl methacrylic 0.8 1.0 Ion exchange 3 7.3 92 A A 140acid/n-butyl water methacrylate = 40/60 Comparative Methyl methacrylic0.2 0.2 Ion exchange 3 0.3 82 B A 262 Example 1 acid/n-butyl waterComparative methacrylate/ 0.8 0.2 Ion exchange 3 2.2 86 B A 216 Example2 methacrylic water Comparative acid = 39.8/60/0.2 0.2 1.0 No washing 073 100 A C 457 Example 3 Comparative 0.1 0.6 Na2SO4 aqueous 1 3 88 B A550 Example 4 solution [400 ppm]

As it is clearly shown from the results of Table 1, the particles of anacrylic polymer, which have been obtained from Examples 1 to 7 andsatisfy the constitution of the present invention, have electrostaticbuildup inhibition rate of 92% or more, thus showing sufficientlysuppressed electrostatic buildup. Furthermore, the particles of anacrylic polymer, which have been obtained from Examples 1 to 7 and haveNa element amount in a range of 3.5 to 50 ppm, have sufficientlysuppressed electrostatic buildup. Furthermore, the particles of anacrylic polymer obtained from Examples 1 to 7 have excellent fluidity.Furthermore, the particles of an acrylic polymer which have beenobtained from Examples 1 to 7 have excellent solubility in toluene.

On the other hand, the particles of an acrylic polymer obtained fromComparative Examples 1, 2, and 4 have electrostatic buildup inhibitionrate of 88% or less. Furthermore, the particles of an acrylic polymer,which have been obtained from Comparative Examples 1, 2, and 4 and haveNa element amount of 3 ppm or less, exhibit poor fluidity. Furthermore,particles of an acrylic polymer obtained from Comparative Example 3 haveelectrostatic buildup inhibition rate of 100%, but they haveinsufficient solubility in toluene.

INDUSTRIAL APPLICABILITY

According to the present invention, particles of an acrylic polymerhaving excellent fluidity due to suppressed electrostatic buildup, aprocess for producing the particles of an acrylic polymer, an inkcomposition, and a coating composition can be provided. As such, thepresent invention can be suitably utilized in the field of particles ofan acrylic polymer, and thus it is industrially very important.

The invention claimed is:
 1. Particles of an acrylic polymer, comprisinga constituent unit (A) derived from methyl methacrylate and aconstituent unit (B) derived from a (meth)acrylic acid alkyl ester inwhich the alkyl group has 2 to 8 carbon atoms, wherein the particles areformed of one type of acrylic copolymer obtained by a singlepolymerization step, and wherein the particles having electrostaticbuildup inhibition rate of 90 to 99.9% as obtained by the followingmethod: (Method for obtaining electrostatic buildup inhibition rate):According to JIS K 7365:1999 “Plastics Method for determination ofapparent density of material that can be poured from a specifiedfunnel”, volume density (A) of the particles of an acrylic polymer ismeasured, In addition, an anti-static agent is added in an amount of 0.1g per 100 mL of the particles of an acrylic polymer, volume density (B)of a mixture obtained by sufficiently mixing them is measured, and theelectrostatic buildup inhibition rate is calculated based on thefollowing mathematical equation (1).Electrostatic buildup inhibition rate (%)=Volume density(A)/Volumedensity (B)×100  (1)
 2. The particles of an acrylic polymer according toclaim 1, wherein a sodium element amount in the particles of an acrylicpolymer is 3.5 to 50 ppm.
 3. The particles of an acrylic polymeraccording to claim 2, wherein the sodium element amount in the particlesof an acrylic polymer is 3.5 to 30 ppm.
 4. The particles of an acrylicpolymer according to claim 1, wherein the particles have a mass averageparticle diameter of 100 to 1000 μm.
 5. The particles of an acrylicpolymer according to claim 1, further comprising a constituent unit (C)derived from α,β-unsaturated carboxylic acid.
 6. Particles of an acrylicpolymer, comprising a constituent unit (A) derived from methylmethacrylate and a constituent unit (B) derived from (meth)acrylic acidalkyl ester in which the alkyl group has 2 to 8 carbon atoms, theparticles having a sodium element amount of 3.5 to 50 ppm, wherein theparticles are formed of one type of acrylic copolymer obtained by asingle polymerization step.
 7. The particles of an acrylic polymeraccording to claim 6, wherein the sodium element amount in the particlesof an acrylic polymer is 3.5 to 30 ppm.
 8. The particles of an acrylicpolymer according to claim 6, wherein the particles have a mass averageparticle diameter of 100 to 1000 μm.
 9. The particles of an acrylicpolymer according to claim 6, further comprising a constituent unit (C)derived from α,β-unsaturated carboxylic acid.
 10. A process forproducing particles of an acrylic polymer according to claim 1, theprocess comprising a step of washing the acrylic polymer obtained bysuspension polymerization so as to have a sodium element amount of 3.5to 50 ppm.
 11. The process for producing particles of an acrylic polymeraccording to claim 10, wherein a dispersion agent containing sodiumelement is used for the suspension polymerization.
 12. The process forproducing particles of an acrylic polymer according to claim 11, whereina use amount of the dispersion agent is an amount allowing that thesodium element amount contained in the dispersion agent is 0.0009 to0.004 part by mass relative to 100 parts by mass of a raw materialmonomer of the particles of an acrylic polymer.
 13. The process forproducing particles of an acrylic polymer according to claim 10, whereina dispersion aid containing sodium element is used for the suspensionpolymerization.
 14. The process for producing particles of an acrylicpolymer according to claim 13, wherein a use amount of the dispersionaid is an amount allowing that the sodium element amount contained inthe dispersion aid is 0.06 to 0.35 part by mass relative to 100 parts bymass of a raw material monomer of the particles of an acrylic polymer.15. The process for producing particles of an acrylic polymer accordingto claim 10, wherein the washing is carried out by using an aqueoussolution of a sodium element-containing compound.
 16. The process forproducing particles of an acrylic polymer according to claim 15, whereina use amount of the aqueous solution of a sodium element-containingcompound is an amount allowing that the sodium element amount containedin the aqueous solution of a sodium element-containing compound is 0.03to 0.1 part by mass relative to 100 parts by mass of the acrylicpolymer.
 17. The process for producing particles of an acrylic polymeraccording to claim 15, wherein mass of the aqueous solution of a sodiumelement-containing compound to be used for the washing is 1 to 3 timesthe acrylic polymer.
 18. An ink composition, comprising the particles ofan acrylic polymer according to claim
 1. 19. A coating composition,comprising the particles of an acrylic polymer according to claim
 1. 20.An article, comprising the coating composition of claim 19, wherein thearticle is a container, marine article, or a road marking.